BackgroundTyrosinase is a bifunctional enzyme that catalyzes both the hydroxylation of monophenols to o-diphenols monophenolase activity and the subsequent oxidation of the diphenols to o-quinones diphenolase activity. Due to the potential applications of tyrosinase in biotechnology, in particular in biocatalysis and for biosensors, it is desirable to develop a suitable low-cost process for efficient production of this enzyme. So far, the best production yield reported for tyrosinase was about 1 g L, which was achieved by cultivating the filamentous fungus Trichoderma reesei for 6 days.

ResultsIn this work, tyrosinase from Verrucomicrobium spinosum was expressed in Escherichia coli and its production was studied in both batch and fed-batch cultivations. Effects of various key cultivation parameters on tyrosinase production were first examined in batch cultures to identify optimal conditions. It was found that a culture temperature of 32 °C and induction at the late growth stage were favorable, leading to a highest tyrosinase activity of 0.76 U mL. The fed-batch process was performed by using an exponential feeding strategy to achieve high cell density. With the fed-batch process, a final biomass concentration of 37 g L based on optical density and a tyrosinase activity of 13 U mL were obtained in 28 hours, leading to a yield of active tyrosinase of about 3 g L. The highest overall volumetric productivity of 103 mg of active tyrosinase per liter and hour corresponding to 464 mU L h was determined, which is approximately 15 times higher than that obtained in batch cultures.

ConclusionsWe have successfully expressed and produced gram quantities per liter of active tyrosinase in recombinant E. coli by optimizing the expression conditions and fed-batch cultivation strategy. Exponential feed of substrate helped to prolong the exponential phase of growth, to reduce the fermentation time and thus the cost. A specific tyrosinase production rate of 103 mg L h and a maximum volumetric activity of 464 mU L h were achieved in this study. These levels have not been reported previously.